the diamond ; second, the gem ; and third, the jewelry grinders.
The diamond grinder divides his work into—a, slitting or cleaving ; b, cutting ; c, grinding ; and d, polishing.
Before
operating upon diamonds, some preliminary experiments as to their
soundness are made : for very fine imperceptible fissures may, at the
end of a laborious grinding, terminate either in cracking or spoiling
the stone. An examination for this purpose is made in one of the two
following modes : either the diamonds, or any other gems to be
examined, are steeped in Canada balsam, or in oil of sassafras or
aniseed, in which fluid they are well turned around, whereby the
minutest fissure, on account of its changed refraction of light from
that of the rest of the stone, may be detected ; or the diamond is
exposed to a great heat, and is then thrown into water, when it will
crumble to pieces should any cracks exist within it. The diamond,
although the hardest of all known substances, may yet, with facility,
be cloven with steel tools, the blow being properly applied. The
octahedrons are best fitted for cleaving : they are generally, however,
somewhat rounded, and in order to cleave them, those, planes which are
to be cloven, are left bare, and the rest is coated with a •composition
of resin and brick-dust ; the bare plane is now rubbed with another
sharjt-edged diamond until a
